Java uses wrapper classes because basic data types cannot directly participate in object-oriented operations, and object forms are often required in actual needs; 1. Collection classes can only store objects, such as List
Wrapper Classes in Java solve the problem that basic data types cannot directly participate in object-oriented operations. Simply put, we need to wrap classes because some Java mechanisms and APIs require the use of objects rather than primitive types . For example, collection classes (such as ArrayList, HashMap), generics, and scenarios that require null value representation.
1. Collection classes can only store objects
Java's collection frameworks (such as List, Set, Map) can only store objects and cannot directly store basic types such as int and double. If you write an ArrayList<int></int> , the compiler will report an error. At this time, you need to use packaging classes such as Integer and Double.
List<Integer> numbers = new ArrayList<>(); numbers.add(5); // Automatic boxing, the bottom layer is actually new Integer(5)
Although it looks like an int is stored, it is actually an autoboxing mechanism that helps you convert. This code cannot be implemented without the wrapper class.
2. Generics do not support basic types
Java's generic mechanism requires that the type parameter must be a reference type. That is, you can't write like this:
public class Box<int> { ... } // Compile error!And you can write this:
public class Box<Integer> { ... }If you want a class to handle multiple numeric types, or use them as a general container, you must use wrapper classes to meet the requirements of generics.
3. Indicates "null value" or "missed value"
Basic types have default values, for example, int defaults to 0, boolean defaults to false. But in some business logic, we want to express the meaning of "this value has not been set" or "not existed". null is very useful at this time.
For example, a field in a database query may be NULL, it is more appropriate to use Integer instead of int:
Integer age = getAgeFromDatabase(); // can return null
If it is an int type, you cannot distinguish between "age is 0" and "data not found".
4. Tool method and string conversion
The wrapper class provides many practical methods, such as converting a string to the corresponding basic type:
String str = "123";
int num = Integer.parseInt(str);
double d = Double.parseDouble("3.14");These methods are very common when processing user input, reading configuration files, and parsing JSON data. If there is no wrapper class, these functions must be implemented by themselves or rely on third-party libraries.
Basically these are the reasons. Packaging classes exist not to replace basic types, but to make up for their shortcomings in the object-oriented world. Although packaging classes will bring some performance overhead (such as greater memory footprint and loss of unboxing), in modern JVMs, this impact is already very small and can be used with confidence most of the time.
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